testing: misc work on test coverage (#201758)

- Allow coverage bar color thresholds to be configurable as the Java
  folks requested.
- Update some of our scripts for integration into
  the selfhost test runner.
- Initial parts of showing function coverage in the Test Coverage view.
  (Still a work in progress, more tomorrow)

test/unit/node/index.js

@@ -23,7 +23,7 @@ const { takeSnapshotAndCountClasses } = require('../analyzeSnapshot');
  */
 const args = minimist(process.argv.slice(2), {
 	boolean: ['build', 'coverage', 'help'],
-	string: ['run'],
+	string: ['run', 'coveragePath'],
 	alias: {
 		h: 'help'
 	},
@@ -36,6 +36,7 @@ const args = minimist(process.argv.slice(2), {
 		build: 'Run from out-build',
 		run: 'Run a single file',
 		coverage: 'Generate a coverage report',
+		coveragePath: 'Path to coverage report to generate',
 		help: 'Show help'
 	}
 });
@@ -141,7 +142,7 @@ function main() {
 			if (code !== 0) {
 				return;
 			}
-			coverage.createReport(args.run || args.runGlob);
+			coverage.createReport(args.run || args.runGlob, args.coveragePath);
 		});
 	}